WO 2011/042369 discloses a method of controlling a wind turbine, where a control signal for a controllable parameter of the wind turbine is determined, and the rotor power coefficient, the torque coefficient, and/or a thrust coefficient of the wind turbine are estimated at time intervals. From this is determined a variation parameter reflecting the variation of the estimated rotor power, torque or thrust coefficient over time. The wind turbine is then controlled according to the control signal only if the variation parameter is above an alert threshold, and otherwise according to a modified control strategy. The control signal may have a power or torque reference signal for controlling the rotational speed of the turbine or a blade pitch reference signal. The modified control method may for instance entail stopping or de-rating the wind turbine. A control system configured to perform the above control method, and a wind turbine comprising such system are also disclosed. This document disclose page 5 line 9-30 “A control method based directly on the measured or estimated wind speed may similarly be inaccurate and unsuitable, as the controlling is then based on the wind speed in one point in space only and as changes to this parameter may not reflect similar changer in the overall wind speed”.